Problem with Rewrite in htaccess

[jullebarge]

Hello,

My website has a dynamic signature generator at this adress:
http://wotskins.x10.bz/sign/sign.htm

This part of my website rely on a htaccess file that allow me to use adress ending with a filename .png beeing processed as php files (they are in fact php files).
My htaccess is this one:

RewriteEngine On
RewriteBase /
RewriteRule ^(.+)-(.+)\.png$ stats.php?username=$1&fond=$2 [L]

This perfectly work in wamp on my computer but when I upload my website, it doesn't work, I get a 404 error when the picture is created.

How can I solve this problem ?